Package structure for optical element and fibers and composite structure thereof

ABSTRACT

An optical element-optical fiber composite structure having a high resistance of the optical fiber to breakage due to cyclical change in temperature, includes a package structure having a main container, side containers attached to the main container and sleeves through which a main chamber of the main container is connected to side chambers of the side containers; an optical element housed in the main chamber; and optical fibers introduced into the main chamber through the side chambers and the sleeves and connected to the optical element.

This application is a divisional of application Ser. No. 08/362,190,filed Dec. 22, 1994, U.S. Pat. No. 5,603,036.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a package structure for housing anoptical element and gas-hermetically sealing optical fibers connected tothe optical element, and a composite structure of an optical element andoptical fibers housed and gas-hermetically sealed in the above-mentionedpackage structure.

The package structure and the optical element-optical fiber compositestructure of the present invention are useful for optical devicescomprising an optical waveguide electro-optical element.

2. Description of the Related Art

In a conventional optical element-optical fiber composite structure inwhich an optical element is housed and gas-hermetically sealed in apackage, a pair of optical fibers are connected to the optical elementand extended to the outside of the package through sleeves attached tothe package, and the sleeves are gas-hermetically sealed. Usually, eachoptical fiber comprises a naked core fiber, and coating layerscomprising a primary coat layer formed on the naked core fiber and asecondary coat layer formed on the primary coat layer. When the opticalfiber is connected to the optical element, at an end portion of theoptical fiber, the coating layer is removed so as to expose the nakedcore fiber to the outside, and a portion of the naked core fiberadjacent to a portion of the optical fiber coated with the coating layeror the primary coat layer is surface-metallized with a metal, forexample, nickel and gold. A terminal face of the naked fiber portion isconnected to a terminal face of the optical element through an adhesive,and the surface-metallized fiber portion is bonded to the sleeve with amoisture-nonpermeable bonding material, for example, solder. Namely, agap between the peripheral surface of the surface-metallized fiberportion of the optical fiber located in the sleeve and an insideperipheral surface of the sleeve is sealed by the solder.

Usually, the soldered surface-metallized fiber portion of the opticalfiber exhibits a relatively low tensile strength of 0.5 to 1.5 kgf. Anideal tensile strength of the core fiber is about 6 kgf. Reasons for thereduction in the tensile strength of the soldered core fiber portion areassumed that microcracks are unavoidably formed on the naked core fiberportion while the coating layer is removed, a surface metallization isapplied to the naked core fiber portion surface and soldering is appliedto the surface-metallized core fiber portion.

Therefore, it is practically difficult to enhance the tensile strengthof the soldered portion of the surface-metallized core fiber portion.However, this tensile strength, namely a seal-fixing strength of theoptical fiber to the package, is unsatisfactory.

In a prior art, an attempt was made in which a portion of the opticalfiber having the coating layer is inserted into the sleeve and thecoating layer is bonded to the inside peripheral surface of the sleeve,to enhance the seal-fixing strength of the optical fiber to the package.

Nevertheless, this attempt is disadvantageous in that generally, thecoating layer and the core fiber are significantly different inexpansion coefficient from each other, namely the core fiber has anexpansion coefficient of one tenth (1/10) or less that of the coatinglayer, the coating layer retains a stress generated during the formationthereof, and therefore, when a heating and cooling are cyclicallyapplied to the optical fiber, the coating layer is expanded and shrunkto an extent larger than that of the core fiber. If the interfacialbonding strength between the coating layer and the core fiber is low, itappears that the core fibers are pushed out from the coating layer whenthe coating layer shrinks and are pulled into the coating layer when thecoating layer expands. The pushing and pulling distance of the corefiber due to the above-mentioned phenomenon is variable depending on thetype and the material of the coating layer. When the secondary coatlayer is made of a polyamide resin, the pushing and pulling length ofthe core fiber sometimes reaches more than several hundred μm withintemperature range of -20° and 70° C. Also it is practically impossibleto eliminate this phenomenon.

In the above-mentioned type of sealing manner of the optical fiber tothe sleeve, the optical fiber is fixed at two portions thereof spacedfrom each other, namely at the soldered portion of thesurface-metallized fiber portion and the adhesive-bonded portion of thecoating layer-coated portion. Where the core fiber pushed out from thecoating layer, a non-fixed portion of the core fiber between the twofixing points is bent in the sleeve, and sometimes is broken by acompression buckling thereof due to a buckling stress (localized tensilestress) generated therein.

In practical use, the surface of the core fiber located in the sleeve issometimes gradually corroded, and thus the buckling stress generated inthe core fiber causes the corroded core fiber to be broken.

Accordingly, there is a strong demand for preventing the generation ofthe buckling stress in the core fiber.

To prevent the breakage of the core fiber due to the buckling stress, ithas been attempted to make the distance between the fixing points of theoptical fiber large enough to absorb and relax the deformation of thecore fiber. However, this attempt was not successful because the largedistance between the fixing points causes the resultant packagestructure for the optical element and the optical fibers to have toolarge a size.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a package structure forhousing an optical element and gas-hermetically sealing optical fibersconnected to the optical element, capable of preventing breakage of theoptical fibers by a buckling stress generated due to change inenvironmental temperature, and a composite structure of an opticalelement and optical fibers housed and gas-hermetically sealed in thepackage structure.

The above-mentioned object can be attained by the package structure andthe optical element-optical fiber composite structure of the presentinvention.

The package structure of the present invention for housing an opticalelement and gas-hermetically sealing optical fibers connected to theoptical element, comprises

a main container provided with a main chamber for housing an opticalelement therein;

a pair of side containers attached to the main container and providedwith a pair of side chambers formed therein and separated from the mainchamber through a pair of side walls, and having a pair of aperturesthrough which the side chambers are connected to the outside of the sidechambers; and

a pair of sleeves extending from or across the side walls and providedwith a pair of hollow spaces through which the main chamber is connectedto the side chambers;

said apertures and side chambers of the side containers and said hollowspaces of the sleeves being suitable for introducing a pair of opticalfibers into the main chamber of the main container therethrough, toconnect the optical fibers to the optical element.

In the present invention, the package structure is used to form anoptical element-optical fiber composite structure.

In this composite structure of an optical element and optical fibershoused and gas-hermetically sealed in the package structure, an opticalelement is housed in the main chamber; end portions of optical fiberswhich comprise secondary coat sections thereof composed of core fibersand primary and secondary coatings, primary coat sections thereofcontinued from the secondary coat sections and composed of core fibersand primary coatings, surface-metallized core fiber sections thereofcontinued from the primary coat sections and composed ofsurface-metallized core fibers, and naked core fiber sections thereofcontinued from the surface-metallized core fiber sections and composedof naked core fibers, are introduced into the main chamber through theapertures and side chambers of the side containers and the hollow spacesof the sleeves; the terminal faces of the naked core fiber sections areconnected to the terminal faces of the optical element; moieties of thesurface-metallized core fiber sections located in the hollow spaces ofthe sleeves are fixed to the sleeves through moisture-non-permeablebonding material layers formed in gaps between the surface-metallizedcore fiber moieties and the inside peripheral surfaces of the sleeves;and moieties of the secondary coat sections located in the apertures ofthe side containers are fixed to the side containers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory cross-sectional front view of a conventionaloptical element-optical fiber composite structure housed in aconventional package structure;

FIG. 2 is an enlarged explanatory cross-sectional view of a sleeveportion of the conventional composite package structure of FIG. 1;

FIG. 3 is an explanatory cross-sectional front view of a right halfportion of an embodiment of the optical element-optical compositestructure containing the package structure of the present invention;

FIG. 4 is an explanatory cross-sectional front view of a right halfportion of another embodiment of the optical element-optical fibercomposite structure containing the package structure of the presentinvention;

FIG. 5 is an explanatory perspective view of a hood member for forming aside container;

FIG. 6 is an explanatory perspective view of another hood member forforming a side container;

FIG. 7 is an explanatory front view of another embodiment of the packagestructure of the present invention;

FIG. 8 is an explanatory partially cross-sectional plane view of anotherembodiment of the optical element-optical fiber composite structureusing the package structure of FIG. 7, of the present invention;

FIG. 9 is an explanatory partially cross-sectional plane view of a lefthalf portion of another embodiment of the optical element-optical fibercomposite structure of the present invention;

FIG. 10 is an explanatory partially cross-sectional plane view ofanother embodiment of the optical element-optical fiber compositestructure of the present invention;

FIG. 11 is an explanatory plane view of another embodiment of thepackage structure of the present invention from which a lid is omitted;

FIG. 12 is an explanatory cross-sectional front view of the packagestructure of FIG. 11 along a line X--X;

FIG. 13 is an explanatory plane view of another embodiment of theoptical element-optical fiber composite structure containing the packagestructure of FIGS. 11 and 12, from which a lid is omitted;

FIG. 14(A) is an explanatory plane view of an embodiment of the maincontainer usable for the present invention, from which a lid is omitted;

FIG. 14(B) is an explanatory front view of the main container of FIG.14(A);

FIG. 14(C) is an explanatory side view of the main container of FIGS.14(A) and 14(B);

FIG. 15(A) is an explanatory plane view of an embodiment of the sidecontainers usable for the main container of FIG. 14 of the presentinvention, from which lids are omitted;

FIG. 15(B) is an explanatory front view of the side containers of FIG.15(A);

FIG. 15(C) is an explanatory side view of the side containers of FIGS.15(A) and 15(B);

FIG. 16(A) is an explanatory plane view of another embodiment of theoptical element-optical fiber composite structure of the presentinvention containing the container structure of FIGS. 14(A) to 15(C),from which lids are omitted;

FIG. 16(B) is an explanatory back view of the optical element-opticalfiber composite structure of FIG. 16(A);

FIG. 17 shows a relationship between a center line of a sleeve and anaxial line of an optical element of another embodiment of the opticalelement-optical fiber composite structure of the present invention;

FIG. 18 shows an explanatory cross-sectional front view of an embodimentof the optical element-optical fiber connection in the main container ofthe present invention in which the optical fibers are connected at aninclined angle to an axial line of the optical element;

FIG. 19 is an explanatory cross-sectional front view of portions of themain container of the present invention in which the center lines ofsleeves attached to the main container inclines to an axial line of theoptical element;

FIG. 20 is an explanatory cross-sectional front view of a conventionalconnection between an optical fiber and an optical element;

FIG. 21 is an explanatory cross-sectional front view of an embodiment ofthe improved connection of the present invention between an opticalfiber and an optical element;

FIG. 22 is an explanatory cross-sectional front view of anotherembodiment of the improved connection between an optical fiber and anoptical element;

FIG. 23(A) is an explanatory plane view of another embodiment of a righthalf portion of a main container usable for the present invention, fromwhich a lid member is omitted;

FIG. 23(B) is an explanatory cross-sectional front view of the maincontainer of FIG. 23(A);

FIG. 24(A) is an explanatory cross-sectional view of a portion of a maincontainer usable for the present invention;

FIG. 24(B) is an explanatory cross-sectional view of a core fibersection of an optical fiber fixed to the main container of FIG. 24(A);

FIG. 25(A) is an explanatory cross-sectional view of a portion of a maincontainer usable for the present invention;

FIG. 25(B) is an explanatory over view of a portion of the maincontainer of FIG. 25(A);

FIG. 26 is an explanatory cross-sectional front view of anotherembodiment of the main chamber and a composite sleeve usable for thepackage structure of the present invention;

FIG. 27 is an explanatory cross-sectional front view of anotherembodiment of the main chamber and another composite sleeve usable forthe package structure of the present invention; and

FIG. 28 is an explanatory cross-sectional front view of anotherembodiment of the main container and another composite sleeve usable forthe container structure of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a cross-sectional view of a conventional opticalelement-optical fiber composite structure in which an optical element ishoused in a package and optical fibers connected to the optical elementare gas-hermetically sealed.

In FIG. 1, a container 1 is a hexahedron box composed of a receptaclemember 2 and a lid member 3 with which the receptacle member 2 isgas-hermetically sealed, for example, by seam welding. In the receptaclemember 2, an optical element 5 is housed and fixed in an inside chamber4 of the receptacle member 2.

A pair of side wall portions 6a and 6b of the container 1 face eachother and are provided with a pair of apertures 7a and 7b formedtherein. Into the apertures 7a and 7b, a pair of sleeves 9a and 9bhaving hollow spaces (not shown in FIG. 1) for passing a pair of opticalfibers 8a and 8b therethrough, are inserted and fixed. The opticalfibers each have a core fiber and a coating layer comprising a primarycoat layer formed on the core fiber and a secondary coat layer formed onthe primary coat layer. In FIG. 1, the optical fibers 8a and 8b areinserted into the hollow spaces of the sleeves 9a and 9b in such amanner that in each optical fiber, an end portion 11a or 11b consistingof the core fiber enters from the sleeve 9a or 9b into the insidechamber 4 and another portion 10a or 10b in which the core fiber iscoated by the coating layer is introduced into the hollow space of thesleeve 9a or 9b.

In the portions of the optical fibers 8a and 8b entered into the insidechamber 4, the primary and secondary coat layers are removed so that theremaining core fibers 11a and 11b are exposed to the outside, and theperipheral surfaces of the exposed core fibers 11a and 11b are plated ormetallized with a metal, for example, gold or a bi-layer of gold andnickel. Portions of the surface-metallized core fiber portions 11a and11b located in the hollow spaces of the sleeves 9a and 9b are bonded tothe inside peripheral surfaces of the sleeves 9a and 9b with solder soas to seal gaps between the optical fiber portions 11a and 11b and theinside peripheral surfaces of the sleeves 9a and 9b. Namely, the opticalfiber portions located in the sleeves are gas-hermetically sealed. Inthe prior arts, generally, the surface-metallized core fiber portions11a and 11b located in the inside chamber 4 are bent or curved asindicated in FIG. 1, and the terminal faces of the core fibers 11a and11b are connected to terminal faces of the optical element 5. Theconnecting portions are protected and reinforced by optical fiberconnection-reinforcing devices 12a and 12b such as glass capillaries.

FIG. 2 shows an enlarged cross-sectional view of the sleeve and theoptical fiber portion inserted into the sleeve, as shown in FIG. 1. InFIG. 2, a sleeve 9a having a hollow space 13 is inserted through a sidewall 6a of a container. An optical fiber 8a has a coating layer-coatedportion 10a, a primary coat layer-coated portion 14 and asurface-metallized core fiber portion 11a, and is inserted into thesleeve 9a. The coating layer-coated portion 10a of the optical fiber 8ais located in an inlet portion of the sleeve 9a and bonded to the sleeve9a by a bonding material 16 such as an epoxy adhesive material. Thesurface-metallized core fiber portion 11a of the optical fiber 8a isfixed in an outlet portion of the sleeve 9a with solder 15.

Namely, the optical fiber portion located in the sleeve is fixed at twopoints spaced from each other.

As mentioned above, in the conventional optical element-optical fibercomposite structure, the surface-metallized core fiber portion 11a ofthe optical fiber 8a located in the hollow space 13 of the sleeve 9a isbent or curved as shown by broken lines when the core fiber portion 11ais heated and cooled, and protrudes, and this phenomenon causes the corefiber portion to be broken due to a buckling stress generated therein.

In the package structure of the present invention, the package structurecomprises a main container having a main chamber formed therein forhousing an optical element therein; a pair of side containers attachedto the main container and provided with a pair of side chambers formedtherein and separated from the main chamber through a pair of sidewalls, and having a pair of apertures through which the side chambersare connected to the outside thereof; and a pair of sleeves extendingfrom or across the side walls and provided with a pair of hollow spacesthrough which the main chamber is connected to the side chambers.

In the package structure of the present invention, the apertures andside chambers of the side containers and the hollow spaces of thesleeves are suitable to introduce end portions of a pair of opticalfibers into the main chamber of the main container therethrough, toconnect the optical fibers to the optical element placed in the mainchamber.

In the package structure of the present invention, the sleeves mayextend from the side walls separating the side chambers from the mainchamber only in directions opposite to the main chambers. Namely, thesleeves project only into the side chambers.

Also, in the package structure of the present invention, the sidecontainers may be in the form of cylinders surrounding the sleeves.

Alternatively, in the container structure of the present invention, theside containers may be in the form of hexahedrons.

Further, in each side container of the package structure of the presentinvention, a center line of the aperture of the side container and acenter line of the hollow space of the corresponding sleeve opening tothe side chamber of the side container may be laid on one and the samestraight line. In this case, an optical fiber can be introduced in astraight line form into the main chamber through the aperture of theside container and the hollow space of the sleeve.

Alternatively, in each side container of the package structure of thepresent invention, a center line of the aperture of the side containermay intersect a center line of the hollow space of the correspondingsleeve. In this case, an optical fiber introduced into the side chamberof the side container is curved between the aperture of the sidecontainer and the corresponding sleeve. The intersecting angle betweenthe aperture center line and the hollow space center line is preferablymore than zero but not more than 90 degrees, namely, at a right angle oran acute angle.

In the embodiments of the package structure of the present inventionshown in FIG. 3, an optical element 21 is housed in a main chamber 22 ofa main container 23. The main container 23 is composed of a receptaclemember 23a and a lid member 23b. In the receptacle member 23a, a sidewall 23c has an aperture 24. A sleeve 25 is attached to the side wall23c so that a hollow space 26 is connected to the aperture 24 of theside wall 23c. The sleeve 25 extends only outward from the maincontainer 23.

A side container 27 in the form of a cylinder is attached at an insideend thereof to the side wall 23c of the main container 23 so as to coverthe sleeve 25. The side container 27 has a side chamber 28 and theaperture of the side container 27 is an outside end opening 28a of thecylinder.

In the embodiment of the optical element-optical fiber compositestructure of the present invention shown in FIG. 3, an end portion of anoptical fiber 29 is introduced into the main chamber 22 through the sidecontainer 27 and the sleeve 25. In the end portion of the optical fiber29, a coating layer-coated section 29 is located in the outside endopening portion 28a of the side chamber 28, a surface-metallized corefiber section 29b is located in the remaining portion of the sidechamber 28 and the hollow space 26 of the sleeve 25 and further entersinto the main chamber 22. A terminal face of the core fiber is connectedto a terminal face of the optical element 21 to form an opticalconnection 30.

In FIG. 3, the hollow space 26 of the sleeve 25 is sealed with amoisture-non-permeable bonding material 31, for example, solder, so thatthe surface-metallized core fiber section located in the hollow space 26of the sleeve 25 is firmly bonded to the inside peripheral surface ofthe sleeve 25. Also, the side chamber 28 of the side container 27 isfilled with a filler 32, for example, a silicone resin or an epoxyadhesive material, so that the section of the optical fiber 29 locatedin the side chamber 28 is stably held in the side container 27. Also agap between the coating layer-coated section 29a of the optical fiber 29and the inside peripheral surface of the side container 27 is sealed bythe filler. The filler 32 is effectively used to prevent the breakage ofthe core fiber section of the optical fiber 29.

In FIG. 3, the sleeve 25 extends only into the cylindrical sidecontainer 27. In this type of sleeve, the solder sealing at a hightemperature is carried out outside of the main chamber. Therefore, thecore fiber section located in the main chamber is not deteriorated bythe solder-sealing process at a high temperature.

In FIG. 3, the outside end of the sleeve 25 is inclined upward. Theupwardly inclined end of the sleeve 25 effectively receives a soldermelt and smoothly introduces the solder melt into the hollow space 26.

In FIG. 4, a side chamber 34 is in the form of a hexahedron. This sidechamber 34 is composed of a bottom 34a extending outwardly from the sidewall 23c and a hood member 34b attached to the side wall 23c and thebottom 34a and consisting of three walls 34c and a roof 34d. The hoodmember 34b is fixed to the side wall 23c and the bottom 34a by anadhesive material or screws. A side wall of the hood member 34b facingthe side wall 23c of the main container 23 has an aperture for insertingan optical fiber 29.

FIG. 5 shows an example of the hood member 34b. In FIG. 5, the side wall34c has a circular aperture 35. FIG. 6 shows another example of the hoodmember 34b. In the side wall 34c of FIG. 6, the aperture is in the formof a reversed U-shaped channel 36. The lower end of the reversedU-shaped channel 36 is blocked by the bottom (not shown in FIG. 6), toform an aperture. Referring to FIGS. 4, 5 and 6, a gap between theinside peripheral surface of the aperture 35 or 36 and the coatinglayer-coated section 29a of the optical fiber 29 is packed with a resin,for example, a silicone resin or an epoxy adhesive material, to fix theoptical fiber 29 to the side container 34. Also, the side chamber 28 ispacked with a soft filler, for example, a silicone resin or an epoxyadhesive material 32.

In the package structure of the present invention, the main containerand the side container are made from a metal material, for example, astainless steel and the inside peripheral surfaces of the containers arepreferably plated with a nickel and/or gold which enables the insideperipheral surfaces to be soldered.

The core fiber section located in the package structure of the presentinvention is metallized with nickel and/or gold, and the moisturenon-permeable bonding material is preferably a Pb-Sn alloy solder.

Referring to FIGS. 7 and 8, a package structure 37 of the presentinvention comprises a receptacle member 38 and a lid member 39 by whichthe upper opening of the receptacle member 38 is gas-hermeticallysealed. Also, the package structure 37 comprises a main container 40 andside containers 41a and 41b separated from the main container 40 by sidewalls 42a and 42b. The main container 40 has a main chamber 43 and theside containers 41a and 41b have side chambers 43a and 43b. The lidmember 39 may be composed of a lid 44 for the main container 40 and lids45a and 45b for the side containers 41a and 41b. The main container 40has a stand 46 for fixing an optical element 21. In the side walls 42aand 42b, apertures 47a and 47b are formed and sleeves 48a and 48b areinserted into the apertures. In front walls 49a and 49b of the sidecontainers 41a and 41b, apertures 50a and 50b are formed to providepassages for the optical fibers 51a and 51b. The apertures 50a and 50bmay be in the form of slots opening upperward and closed by the lidmembers 45a and 45b.

In FIG. 8, the sleeves 48a and 48b have hollow spaces 52a and 52b. Thecenter line of the hollow spaces 52a and 52b intersect the center lineof the apertures 50a and 50b of the side containers 41a and 41b at anangle θ of more than zero but not more than 90 degrees.

In FIG. 8, end portions of coating layer-coated sections 53a and 53b ofthe optical fibers 51a and 51b are inserted into the apertures 50a and50b, primary coat layer-coated sections 54a and 54b of the opticalfibers 51a and 51b are located in the side chambers 43a and 43b andgradually curved, end portions of the primary coat layer-coated sections54a and 54b are inserted into the hollow spaces 52a and 52b of thesleeves 41a and 41b, and portions of surface-metallized core fibersections 55a and 55b located in the hollow spaces 52a and 52b are fixedto the sleeves 48a and 48b by solder layers 56a and 56b. The endportions of the coating layer-coated sections 53a and 53b of the opticalfibers 51a and 51b inserted into the apertures 50a and 50b are fixed tothe side containers 41a and 41b by adhesive layers 57a and 57b or by amechanical caulking. In this embodiment of the optical element-opticalfiber composite structure shown in FIG. 8, relatively long sections ofthe optical fibers can be contained in the side containers withoutexcessively deforming the optical fibers. This feature is effective toprevent the buckling breakage of the core fiber sections of the opticalfibers located in the hollow spaces of the sleeves, due to the pushingout phenomenon of the core fiber sections. Preferably, the length of theprimary coat layer-coated section of the optical fiber located in agradually curved form in the side container is in the range of from 20to 50 mm.

In the package structure shown in FIGS. 7 and 8, the side containers maybe separable from the main container. In the preparation of the opticalelement-optical fiber composite structure by using the separable packagestructure, the optical element is placed and fixed in the main chamberof the main container, the core fiber sections of the optical fibers areintroduced into the main chamber through the hollow spaces of thesleeves, and the terminal faces of the core fiber sections are connectedto the terminal faces of the optical element. The core fiber sectionslocated in the sleeves are fixed by solder so as to gas-hermeticallyseal the hollow spaces of the sleeves.

The side containers are attached to the main containers and fixedthereto by an adhesive or screws. The end portions of the coatinglayer-coated sections of the optical fibers are inserted into theapertures of the side chambers and fixed by an adhesive to the sidecontainers so that the primary coat layer-coated sections of the opticalfibers are gradually curved in the side chambers. Finally, the maincontainer and the side containers are gas-hermetically closed by lids.

In FIG. 8, the apertures 50a and 50b of the side containers 41a and 41bare located in the front walls 49a and 49b. However, one of theapertures may be located in a front wall of a side container and theother one of the apertures may be located in a back wall of the otherside container.

In FIG. 9, as shown by solid lines, an aperture is formed in a side wall58 of the side container 41a facing the side wall 42a of the maincontainer 40, and into the aperture, a side container sleeve 59 isinserted and fixed thereto. Into the sleeve 59, an end portion of acoating layer-coated section 53a of an optical fiber 51a is inserted andbonded thereto by an adhesive layer 60. In this embodiment, theintersecting angle θ between the center line of the sleeve 48a of themain container 40 and the sleeve 59 of the side container 41a is lessthan 90 degrees, and thus the primary coat layer-coated section 54a ofthe optical fiber 51a is slightly curved in the side chamber 43a.

In FIG. 9, as shown by broken lines, the aperture and sleeve 61 of theside container 41a are provided in a side wall 62 connected to the sidewall 42a of the main container 40. In this case, the intersecting angleθ between the center line of the main container sleeve 48a and thecenter line of the side containers sleeve 61 is 90 degrees. Referring toFIG. 10, side container sleeves 59a and 59b are arranged at cornersbetween the side wall 58a and 58b, and the side wall 62a and 62b so thatthe intersecting angle becomes less than 90 degrees, for example, about45 degrees.

The side chambers may be packed with a soft resinous filler, forexample, a silicone resin or an epoxy adhesive material, whicheffectively protects the optical fibers in the side containers frommechanical shocks, for example, vibrations.

In an embodiment of the package structure of the present invention, theside chambers of the side containers are connected to each other througha connecting passage arranged outside of the main container. Theconnecting passage allows a pair of optical fibers to be introduced fromone of the side chambers to the other one therethrough.

The above-mentioned type of package structure of the present inventionhas the following advantages.

(1) The optical fibers can be fixed in coating layer-coated sectionsthereof to the side containers, and thus core fiber sections of theoptical fibers located in the main chamber are prevented from harmfulstress and the sealing conditions of the sleeves attached to the maincontainer can be stably maintained at a good level over a long period oftime.

(2) Since sections of the optical fibers between the apertures of theside containers and the sleeves of the main container can be made longand curved, the core fiber sections of the optical fibers located in themain chamber can be prevented from harmful stress and the sealingconditions of the sleeves of the main container can be maintained at agood level with a high degree of stability over a long period of time.

Referring to FIGS. 11 and 12, a package structure 63 of the presentinvention comprises a main container 64 and side containers 65a and 65b.The main container 64 has a main chamber 66 formed therein and the sidecontainers 65a and 65b have side chambers 67a and 67b formed therein.The package structure 63 is further provided with a connecting passage68 formed between a side wall 69 of the main container 64 and aconnecting side wall 70 through which the side containers 65a and 65bare connected to each other. The connecting passage 68 allows the sidechambers 67a and 67b to be connected to each other therethrough.

The side chambers 67a and 67b are separated from the main chamber 66through side walls 71a and 71b. The side containers 67a and 67b haveapertures 72a and 72b formed in side walls 73a and 73b facing the sidewalls 71a and 71b. The main container 64 has sleeves 74a and 74battached to the side walls 71a and 71b. To the apertures 72a and 72b ofthe side containers 65a and 65b, optical fiber-fixing means, forexample, sleeves 75a and 75b are attached.

Referring to FIG. 13, optical fibers 76a and 76b are introduced into thepackage structure 63. End portions of coating layer-coated sections 77aand 77b of the optical fibers 76a and 76b are introduced into theconnecting passage 68 through the optical fiber-fixing means 75a and 75band the side chambers 67a and 67b, and are fixed by the opticalfiber-fixing means 75a and 75b. Primary coat layer-coated sections 78aand 78b extend through the connecting passage 68 and the side chambers67b and 67a, while gradually curving, and are inserted into the sleeves74a and 74b. In the sleeves 74b and 74a, core fiber sections 79a and 79bwhich have been surface-metallized by plating or vacuum-depositing ametal, for example, gold, are gas-hermetically fixed to the sleeves 74band 74a by solder or adhesive, layers 80b and 80a. Naked core fibersections 81b and 81a of the optical fibers 76a and 76b located in themain chamber 66 are optionally slightly curved and connected at terminalfaces thereof to the terminal faces of the optical element. Theconnections of the optical fiber terminal faces to the optical elementterminal faces are protected by protectors 82b and 82a. The main andside containers and the connecting passage are gas-hermetically sealedby a lid (not shown).

Referring to FIGS. 14(A), 14(B) and 14(C), an embodiment of the maincontainer 64 is in the form of a hexahedron and composed of a receptaclemember 83 and a lid member (not shown) for gas-hermetically closing thereceptacle member 83. To a pair of side walls 84a and 84b of thereceptacle member 83, sleeves 74a and 74b are attached. On a front wall85 of the main container 64, a groove 86 is formed as a connectingpassage for the optical fibers.

Referring to FIGS. 15(A), 15(B) and 15(C), side containers 65a and 65bare formed from a bottom plate 87 on which the main container 64 ofFIGS. 14(A) to (C) is also placed, side walls 88a and 88b and lids (notshown). In the side walls 88a and 88b of the side containers 65a and65b, apertures or grooves 89a and 89b are formed. The grooves can beclosed at upper openings thereof by the lids (not shown).

Referring to FIGS. 16(A) and 16(B), the package structure of the presentinvention is formed from the main container as shown in FIGS. 14(A) to(C) and the side containers as shown in FIGS. 15(A) to (C). An opticalfiber 76a is introduced into the main chamber 66 through the aperture89a, the side chamber 67a, the connecting groove 86, the side chamber67b and the sleeve 74b. The other optical fiber 76b is introduced intothe main chamber 66 through the aperture 89b, the side chamber 67b, theconnecting groove 86, the side chamber 67a and the sleeve 74a.

In an embodiment of the package structure of the present invention, withrespect to each sleeve attached to the main container, the center lineof the hollow space of the sleeve intersects an axial line of acorresponding terminal of the optical element fixed in the maincontainer. The intersecting angle between the sleeve hollow space centerline and the optical element terminal axial line is in the range of from2 to 5 degrees.

Usually, where an optical fiber having a coating layer covering a corefiber has a diameter of 0.9 mm, the sleeve for the optical fiber has aninside diameter of about 1 mm. The gap between the inside peripheralsurface of the sleeve and the optical fiber inserted into the sleeve issealed by solder. When a core fiber section having a diameter of 0.125mm of the optical fiber is located in the sleeve and fixed to the sleeveby the solder, the gap between the inside surface of the sleeve and thecore fiber section of the optical fiber is preferably made smaller. Forthis purpose, sometimes, the inside diameter of an end of the sleeveopening to the main chamber is reduced to about 0.6 mm. Usually, thecenter line of the sleeve is parallel to the axial line of the maincontainer.

For example, in a waveguide type electro-optical element which haspotential use as an external modulator for an optical communicationsystem, the connection of the terminal faces of the optical element tothe terminal faces of the optical fibers is carried out by using anadhesive having a low refractive index to reduce a reflection of lightat the connection. Also in the connection, an inclined incidence systemis usually employed.

Where the core fiber section of the optical fiber is introduced into themain chamber through the sleeve having a very small inside diameter, andis connected to the optical element, the core fiber section must be bentso as to impart an inclined incidence angle, for example, 5 to 7degrees, to the axial line of the terminal of the optical element. Thisbending sometimes causes the core fiber section to be brought intocontact with the edge of the sleeve and to be broken or scratched.Accordingly, this connecting operation is not always easy.

The above-mentioned feature of the package structure effectively allowsthe core fiber sections of the optical fibers to be connected to theoptical element at a desired angle, without damaging the core fibersections of the optical fibers.

Referring to FIG. 17, a main container 90 has a sleeve 91, and anoptical element 97 is fixed on a stand 92 in a main chamber 93. Aterminal face 94 of the optical element 97 is inclined at an angle R₁(not shown in FIG. 17), for example, 5 degrees, from a plane 95 crossingat right angles to the axial line 96 of the optical element 97. Also, aterminal face of a glass capillary 98 through which a terminal of anoptical fiber is connected to the terminal face 94 of the opticalelement 97, is inclined at an angle R₂, for example, 7 degrees, from aplane crossing at right angles to the center line of the optical fiberinserted into the capillary 98. In this case, the optical fiber can beconnected to the optical element at an angle of R₂, for example, 7degrees to the terminal face of the optical element, and at an angle ofR₃ =R₂ -R₁, for example, 7-5=2 degrees, to the axial line of the opticalelement.

A center line 99 of the sleeve 91 intersects the axial line 96 of theoptical element 97 at an angle R₃, preferably of 2 to 5 degrees.

Referring to FIG. 18, in a main container 100 having a main chamber 101,an optical element 102 is fixed. A pair of sleeves 103a and 103b areattached to a pair of side walls 104a and 104b facing each other. A pairof optical fibers 105a and 105b are introduced into the main chamber 101through the sleeves 103a and 103b and connected to terminal faces of theoptical element 102. The center lines of the sleeves 103a and 103b areinclined to the axial line of the optical element at a small angle R₃ asshown in FIG. 17.

In FIG. 19, the sleeve attached to the side wall 104a has a center line106a inclined at an angle R_(3a) to a horizontal line 107a parallel toan axial line of an optical element (not shown). Also, the sleeve 103battached to the side wall 104b has a center line 106b inclined at anangle R_(3b) to a horizontal line 107b parallel to the axial line of theoptical element (not shown). The angles R_(3a) and R_(3b) are preferably2 to 5 degrees.

In the above-mentioned connection manner, the core fiber sections of theoptical fibers can be connected to the terminals of the optical elementat a desired incidence angle without breaking or damaging the core fibersections.

When a terminal face of a naked core fiber section of an optical fiberis connected to a terminal face of an optical element, usually, aconnection-reinforcing device is used. The connection-reinforcing deviceis a glass block having a V-shaped groove for receiving the naked corefiber section, or a glass capillary having a hollow space for receivingthe naked core fiber section.

Referring to FIG. 20 showing a conventional connection of an opticalelement to an optical fiber through a glass capillary, a glass capillary108 has a hollow space, and a naked core fiber section 110 of an opticalfiber is inserted into the hollow space 109. The inserted naked corefiber section 110 is bonded to the glass capillary 108 through anadhesive 111. The glass capillary 108 with the naked core fiber section110 is bonded to the terminal face of an optical element 112 with abinder 113. In another manner, the naked core fiber section 110 of theoptical fiber passes through the capillary 108, the terminal face of thenaked core fiber section 110 is connected to the terminal face of theoptical element 112 by an adhesive, the terminal face of the capillary108 is bonded to the terminal face of the optical element 112 by theadhesive, and then the adhesive is injected into the hollow space 109 ofthe glass capillary 108 so as to fix the naked core fiber section 110 tothe inside peripheral surface of the glass capillary 108.

When the connection-reinforcing block having a V-shaped groove is used,a terminal face of the block is bonded to a terminal face of the opticalelement by an adhesive, the naked core fiber section of the opticalfiber is placed in the groove, the terminal face of the naked core fibersection is bonded to the terminal face of the optical element, and thenaked core fiber section in the groove is bonded to the block by anadhesive.

In the above-mentioned conventional manners of connecting the opticalelement to the optical fiber, it is difficult to arrange the terminalface of the capillary on the same plane as that of the terminal face ofthe optical fiber. In this case, usually, the capillary terminal face islocated farther from the terminal face of the optical element than theterminal face of the optical fiber. Namely, as shown in FIG. 20 thedistance D between the terminal face of the optical element and theterminal face of the capillary is larger than the distance d between theterminal face of the optical element and the terminal face of theoptical fiber. Therefore, the capillary cannot fully protect andreinforce the connection between the optical fiber and the opticalelement.

Also, it is difficult to arrange the terminal face of the capillary inparallel to the terminal face of the optical fiber and thus the opticalfiber inserted into the capillary is inclined to the center line of thehollow space of the capillary. In this case, the capillary cannot fullyprotect the optical fiber inserted therein, and the connection betweenthe optical element and the optical fiber becomes unstable.

The above-mentioned disadvantages can be removed by the followingconnection procedures.

Referring to FIGS. 21 and 22, in an end of each optical fiber, aterminal face of a naked core fiber section 110 of the optical fiber isconnected to a terminal face of an optical element 112 through a firstbonding layer 114 consisting of a resinous adhesive and having arefractive index of 1.4 to 1.6, and the first bonding layer 114 iscovered by a second bonding layer 115 consisting of a resinous adhesiveand spreading between the peripheral surface of the end portion of thenaked core fiber section 110 and the terminal face of the opticalelement 112.

In the first bonding layer 114, preferably the terminal face of thenaked core fiber section 110 of the optical fiber is embedded in a topportion of the first bonding layer 114 and thus peripheral surface ofthe embedded portion of the naked core fiber section 110 is covered bythe first bonding layer 114. Also, the first bonding layer 114 is in theform of a substantial circular cone symmetrical around the axial line ofthe naked core fiber section 110.

The circular cone-shaped first bonding layer 114 preferably has adiameter r of the bottom face thereof of 130 to 200 μm.

Also, the distance between the terminal face of the optical element 112and the terminal face of the naked core fiber section 110 is preferablyabout 50 μm or less. Further, the end portion of the naked core fibersection 110 is preferably embedded at a depth of 5 to 50 μm in the firstbonding layer 114 and the first bonding layer preferably has a height L₁of about 50 μm.

The first bonding layer is preferably formed from a resinous adhesivehaving a relatively low viscosity, for example, an ultraviolet rayirradiation-curable adhesive which is useful for forming a circularcone-shaped or bell-shaped bonding layer.

The first bonding layer exhibits a relatively low bonding strength of 2to 3 gf.

In a cross-sectional profile of the first bonding layer, the edge linemay be a straight line or a curved line projecting outward or inward(FIGS. 21 and 22).

Referring to FIGS. 21 and 22, a resinous adhesive is coated on the firstbonding layer 114 to form a second bonding layer 115. Preferably, thesecond bonding layer 115 is in the form of a circular cone or a bellsymmetrical about the axial line of the naked core fiber section 110 ofthe optical fiber. The second bonding layer 115 preferably has adiameter R of the bottom thereof of 500 to 1000 μm and a height L₂ of100 to 1000 μm.

Due to the formation of the second bonding layer on the first bondinglayer, the bonding strength between the optical element and the opticalfiber is enhanced to a high level of 100 to 1000 gf. In thecross-sectional profile of the second bonding layer, the edge line is inthe form of a straight line or a curved line projecting outward (FIG.21) or inward (FIG. 22).

The first bonding layer is formed from a resinous adhesive having arefractive index of 1.4 to 1.6, to provide a good optical connectionbetween the optical element and the optical fiber. The resinous adhesivefor the first bonding layer may be selected from ultraviolet ray-curableepoxy resins and ultraviolet ray-curable acrylate resins for opticaluse.

The second bonding layer is formed from the same resinous adhesive asthat for the first bonding layer or another resinous adhesive softerthan that for the first bonding layer. For example, the soft resinousadhesive for the second bonding layer is selected from silicone resinsand polyurethane resins which are capable of preventing an undesirableconcentration of stress in the connection between the optical elementand the optical fiber.

The connection between a terminal face of an optical element and aterminal face of a naked core fiber section of an optical fiber isreinforced by using a block for supporting the naked core fiber section,or a capillary. The naked core fiber section is inserted into a hollowspace of the capillary, and the terminal face of the capillary isconnected together with the terminal face of the naked core fibersection to the terminal face of the optical element. This connection ofthe capillary is optionally further reinforced by using a block bondedto both the capillary and the optical element. When the block is used,the block must be bonded to a bottom surface of the main container, andthe naked core fiber section is also connected to the optical element.The bonding of the block sometimes reduces the reliability of theresultant optical device.

Also, if the capillary is used, the arrangement of the capillary whichis rigid in the connection between the optical element and the opticalfiber sometimes causes a slight movement of the optical fiber due tovibration, impact or cyclical heating applied to the connection.

The above-mentioned disadvantages can be removed in the followingmanner.

In the main container of the present invention, a first bottom portionon which the optical element is fixed and a pair of second bottomportions located between the optical element and the sleeves areprovided. The upper faces of the second bottom portions are higher thanthe upper face of the first bottom portion and lower than the lowerfaces of the optical fiber sections located above the second bottomportions. Also, moieties of the optical fiber sections are fixed to theupper faces of the second bottom portions by fixing means.

Preferably, the moieties of the optical fiber sections located above thesecond bottom portions are moieties of surface-metallized core fibersections and are fixed to the upper faces of the second bottom portionswith solder layers surrounding the moieties of surface-metallized corefiber sections. Alternatively, the moieties of the optical fibersections located above the second bottom portions are moieties of thenaked core fiber sections and are fixed to the upper faces of the secondbottom portions with a resinous adhesive layers surrounding the nakedcore fiber moieties. Preferably, in each second bottom portion, thedistance between a connecting terminal face of the optical element andan end of the second bottom portion closest to the optical element is 5mm or less, measured in parallel to the upper face of the first bottomportion.

FIGS. 23(A) and 23(B) show a right half portion of a main chamber of thepresent invention in which an optical fiber is connected to an opticalelement.

In FIGS. 23(A) and 23(B), a main container 116 is formed from areceptacle member 117 and a lid member 118 and has a main chamber 119. Abottom 120 of the receptacle member 117 has a first bottom portion 121,on which an optical element 122 is fixed, and a second bottom portion123 facing a passage of an optical fiber 124 connected to the opticalelement 122.

The second bottom portion 123 has an upper face thereof higher than thatof an upper face of the first bottom portion 121. The upper face of thesecond bottom portion 123 is spaced from a lower face of the passage ofthe optical fiber 124. Namely, the upper face of the second bottomportion 123 is lower than and spaced from the lower face of the opticalfiber passage. A section 124a of the optical fiber 124 located in themain chamber 119 consists of a naked core fiber. A terminal face of thenaked core fiber section 124a is connected to a terminal face of theoptical element 122, and the connection is reinforced by a connectingadhesive layer 125 and a reinforcing block 126. Usually, the surface ofthe core fiber section 124a is metallized with gold, nickel or abi-layer of gold and nickel.

A side wall 127 has an aperture and a sleeve 128 is inserted into theaperture. An end portion of a coating layer coating section 124b of theoptical fiber 124 is inserted into a hollow space of the sleeve 128.This section 124b continues to the core fiber section 124a. A moiety ofthe core fiber section 124a located in the hollow space of the sleeve128 is fixed to the inside peripheral surface of the sleeve 128 bysolder 129. Accordingly, the hollow space of the sleeve 128 iscompletely sealed by the solder 129.

A moiety of the core fiber section 124a located immediately above thesecond bottom portion 123 is fixed to the upper face of the secondbottom portion 123 by a fixing means 130 surrounding the moiety of thecore fiber section 124a. The fixing means 130 may comprise solder or aresinous adhesive.

A portion of the bottom 117 between the side wall 127 and the secondbottom portion is not limited to a specific form and dimensions. In FIG.23(B), this bottom portion is formed lower than the first bottom portion121. However, this bottom portion may have the same level as that of thefirst bottom portion 121.

Referring to FIGS. 24(A) and 24(B), a gap S between the upper face ofthe second bottom portion 123 and the lower face of the core fibersection 124 of the optical fiber, a height H of a center line 131 of thecore fiber section 124a from the upper face of the first bottom portion121, a height h of the second bottom portion upper face from the firstbottom portion upper face, and a diameter R of the core fiber section124a have the following relationship:

    S =H-h-R/2

To avoid that the core fiber section being brought into contact with thesecond bottom portion and damaged, S is preferably adjusted to a levelof 100 μm or more. Also, H is preferably almost equal to the thicknessof the optical element, and R is usually 125 μm. When the values of S, Hand R are established, it is easy to establish the value of h.

In FIG. 24(A), a distance L between the terminal face of the opticalelement 122 and an end of the second bottom portion 123 closest to theoptical element 122 is established so that the connecting operation ofthe terminal face of the optical element 122 to the terminal face of thecore fiber section 124a of the optical fiber can be easily carried out,the optical element 122 can be easily fixed to the first bottom portion,and the soldering operation of the core fiber section to the secondbottom portion can be carried out while preventing an undesirableinfluence on the optical element-optical fiber connection. Preferably,the distance L is 5 mm or less, more preferably 2 to 5 mm. Usually, themain container is made from a metal material, for example, a brass,stainless steel or a Kovar steel, and the core fiber is made fromquartz. The difference in thermal expansion between the metal materialsand quartz is in the order of 10⁻⁵ /° C.

If the optical element structure is used in an environment in which achange in temperature is about 100° C., the distance L is preferably 5mm or less to restrict the change in length of the core fiber section toa level of several μm.

Referring to FIGS. 25(A) and 25(B), the second bottom portion 123 isformed by a bottom face of a groove 131 of a projection 132. The corefiber section 124a of the optical fiber passes across the groove 131 andis fixed to the groove 131 by fixing means 130. In this case, the amountof the fixing means 130 applied to the core fiber section 124a of theoptical fiber can be easily controlled by the groove 131 having a knowndepth, width and length.

In an embodiment of the package structure of the present invention, eachsleeve comprises an outer tube extending through and fixed to the sidewall of the main container, an intermediate tube inserted into the outertube and an inner tube inserted into the intermediate tube and having ahollow space allowing the optical fiber to be inserted thereinto andconnected to the main chamber of the main container. This type of sleeveis contributory to making the total length of the package structureshorter. Also, the sleeve effectively shortens the length of a portionof the optical fiber located in the main chamber of the packagestructure. In FIG. 26, a main container 140 is composed of a receptaclemember 141 and a lid member 142 and is provided with a main chamber 143.An optical element 144 is fixed together with a connection-reinforcingblock 145 on a bottom of the receptacle member 141.

An aperture 146 is formed in a side wall 147 of the receptacle member141.

An end portion of an optical fiber 148 comprises a naked core fibersection 149, a surface-metallized core fiber section 150 and a coatingfiber-coated section 151.

A sleeve 152 is composed of an outer tube 153 having an annularprojection 154, an intermediate tube 155 having an annular projection156, and an inner tube 157.

The outer tube 153 is inserted into the aperture 146 andgas-hermetically bonded at the annular projection 154 to the side wall147 of the main container 140 with an adhesive or solder 158.

The end portion of the optical fiber 148 is passed through theintermediate tube 155 and then through the inner tube 157, and a moietyof the coating layer-coated section 151 and a moiety of thesurface-metallized core fiber section 150 continued to the moiety of thesection 151 is located in the hollow space of the inner tube 157. Anadhesive material 159 is applied into the hollow spaces of the innertube 157 to fix the moiety of the surface-metallized core fiber section150 to the inner tube 157.

The inside diameter of the outer tube 153 is established so that the endportion of the optical fiber 148 can be easily introduced into the mainchamber 143, the optical axis of the optical fiber can be aligned withthe optical axis of the optical element 144, and a terminal face of theoptical fiber can be connected to a terminal face of the opticalelement. For this purpose, the inside diameter of the outer tube 153 ispreferably larger than the outside diameter of the inner tube 157.

The naked core fiber section 149 of the optical fiber 148 is introducedinto the main chamber 143 through the outside tube 153, the terminalmoiety of the naked core fiber section 149 is position-adjusted so thatthe optical axis of the terminal moiety of the naked core fiber section149 can be aligned with the optical axis of the terminal portion of theoptical element 144, and a terminal face of the naked core fiber section149 can be connected to a terminal face of the optical element 144. Theconnection is fixed and reinforced by the reinforcing block 145. Theinner tube 157 is located in the hollow space of the outer tube 153. Theintermediate tube 155 is inserted and fixed between the outer tube 153and the inner tube 157. The end opening of the outside tube 153 locatedin the main chamber 143 is sealed with solder. Also, portions of theouter, intermediate and inner tubes located outside of the maincontainer 140 are completely sealed with an adhesive.

In FIG. 27, the connection of the optical fiber 148 and the opticalelement 144 is reinforced by a reinforcing device, for example, glasscapillary 160 together with the reinforcing block 145. The open end ofthe outer tube 153 located in the main chamber 143 is sealed by a solderlayer 161 through which a moiety of the surface-metallized core fibersection 150 extends and a connection of the inner tube 157 and theintermediate tube 155 is sealed by an adhesive layer 162.

In the assembly as shown in FIG. 27, the distance L_(a) between theconnection between the optical element and the optical fiber and thesolder layer 161 can be relatively short, for example, 2 to 10 mm.Accordingly, this short distance L_(a) advantageously makes thealignment of the optical axis of the optical element with that of theoptical fiber easy.

In FIG. 28, the intermediate tube of the sleeve is composed of anoutside intermediate tube 163 and an inside intermediate tube 164. Theoutside intermediate tube 163 has a hollow space including a portion 165thereof suitable for receiving the inside intermediate tube 164 andanother portion 166 having a smaller diameter than that of theabove-mentioned portion 165 and opening to the main chamber 143. Theoutside intermediate tube 163 is advantageous in that during theconnecting operation of the optical fiber to the optical element, theinside tube 157 including the optical fiber 148 is restricted toexcessively move toward the optical element. The outside intermediatetube 163 and the outside tube 154 are gas-hermetically fixed to eachother with an adhesive. The gap between the outside intermediate tube163 and the inner tube 157 is sealed by inserting the insideintermediate tube 164 thereinto and gas-hermetically fixing them with anadhesive. Therefore, in this type of composite sleeve, the adhesivelayer 162 shown in FIG. 27 can be omitted.

We claim:
 1. A composite structure comprising an optical element,optical fibers connected to the optical element and a package structurecomprising (1) a container provided with a chamber housing the opticalelement therein and having a pair of side walls; and (2) a pair ofsleeves extending from or across the side walls of the container andprovided with a pair of hollow spaces through which a pair of opticalfibers are introduced into the chamber of the container, whereina) eachsleeve comprises an outer tube extending through and fixed to the sidewall, an intermediate tube inserted into the outer tube and an innertube inserted into the intermediate tube and having a hollow spaceallowing each optical fiber to be inserted thereinto and connected tothe chamber of the container; b) each hollow space of the sleeve has acenter line intersecting an axial line of a corresponding terminal ofthe optical element placed in the chamber; c) an end portion of eachoptical fiber which comprises a secondary coat section thereof composedof a core fiber and primary and secondary coatings, a primary coatsection thereof continued from the secondary coat section and composedof a core fiber and a primary coating, a surface-metallized core fibersection thereof continued from the primary coat section and composed ofa surfaced-metallized core fiber, and a naked core fiber section thereofcontinued from the surface-metallized core fiber section and composed ofa naked core fiber, is introduced into the chamber through the hollowspace of the inner tube of each sleeve; d) a terminal face of the nakedcore fiber section is connected to a terminal face of the opticalelement; e) a moiety of the surfaced-metallized core fiber sectionlocated in the hollow space of the inner tube of each sleeve is fixed tothe sleeve through a moisture-nonpermeable bonding material layer formedin a gap between the surface-metallized core fiber moiety and the insideperipheral surface of the inner tube of each sleeve; f) a moiety of theprimary coat section and a moiety of the surface-metallized core fibersection continuing to the primary coat section moiety of each opticalfiber are located in the inner tube hollow space and thesurface-metallized core fiber section moiety is fixed to the insideperipheral surface of the inner tube through a resinous bonding materiallayer; and g) an open end of each sleeve, through which another moietyof the surface-metallized core fiber section extends into the chamber,is sealed with a solder layer.
 2. The composite structure as claimed inclaim 1, wherein an intersecting angle between the sleeve hollow spacecenter line and the optical element terminal axial line is in the rangeof from 2 to 5 degrees.